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| United States Patent |
5,690,123
|
|
Medina
|
November 25, 1997
|
Method of altering the shape of the cornea
Abstract
A device is provided to plastically change the shape of the cornea by
application of a vacuum. The device has elongated openings that are
connected to a vacuum pump. By placing the device on the surface of the
cornea and then applying a vacuum, a plastic deformation of the area of
the cornea below the openings is achieved. The resulting effect is that
the curvature and the refractive power of the cornea and the eye are
changed. A flatter cornea reduces or corrects myopia or nearsightedness.
Applications extend to correction of all refractive errors: myopia,
hyperopia and astigmatism.
| Inventors:
|
Medina; Antonio (P.O. Box 2355, Costa Mesa, CA 92628)
|
| Appl. No.:
|
680497 |
| Filed:
|
July 15, 1996 |
| Current U.S. Class: |
128/898; 606/166 |
| Intern'l Class: |
A61B 017/00 |
| Field of Search: |
606/166,204.25,1
128/898
|
References Cited
U.S. Patent Documents
| 3074407 | Jan., 1963 | Moon et al. | 606/166.
|
| 4417579 | Nov., 1983 | Soloviev et al. | 606/166.
|
| 4619259 | Oct., 1986 | Graybill et al. | 606/166.
|
| 4688570 | Aug., 1987 | Kramer et al. | 606/166.
|
| 4744362 | May., 1988 | Grundler | 606/166.
|
| 5108412 | Apr., 1992 | Krumeich et al. | 606/166.
|
| Foreign Patent Documents |
| 1068118 | Jan., 1984 | SU | 606/166.
|
Primary Examiner: Thaler; Michael H.
Claims
What is claimed is:
1. A method for altering the shape of the cornea, comprising the steps of:
placing the openings of a vacuum chamber in contact with the surface of the
cornea of the eye;
applying a vacuum to said vacuum chamber, said vacuum being of such
pressure to exert a force towards said vacuum chamber on the portion of
the cornea placed on said openings, said force causing stress and strain
of said portion of the cornea, with said strain being beyond the elastic
range of the cornea;
holding said vacuum for a length of time such that the cornea extends
beyond its elastic range in said openings under the force exerted by said
vacuum.
Description
BACKGROUND OF THE INVENTION
This invention relates to improved means to correct refractive errors of
the eye: myopia, hyperopia and astigmatism. Several attempts have been
made to correct refractive errors by altering the shape of the cornea of
the eye. A procedure called "orthokeratology" has been used for several
decades with limited results. The procedure consists in prescribing a
series of hard contact lenses over an extended period of time when the
curvature of the lenses is progressively changed. The lenses in turn mold
and change the curvature of the cornea.
Orthokeratology is a painful procedure because the lenses worn are a poor
fit to the shape of the cornea since they must necessarily be of a
curvature different than the cornea. Another problem encountered with this
procedure is that unless lenses are worn regularly the curvature of the
cornea reverts to its original value.
Surgical methods to alter the shape of the cornea have been proposed.
Significantly two are currently in use: "radial keratotomy" and
"photo-refractive keratectomy". Radial keratotomy is a procedure by which
the cornea is cut in almost its full depth in a radial pattern. The cuts
cause the cornea to flatten. Myopia is corrected with some success by
radial keratotomy. Hyperopia cannot be corrected. Problems encountered
with this procedure are related to the fact that the cornea is permanently
and irreversibly damaged. A few of the problems reported are glare,
overcorrection, cornea rupture and low vision. Photo-refractive
keratectomy is the most recent procedure. This method uses an excimer
laser to burn part of the exterior of the central cornea, and therefore
flattens it in a more uniform manner than radial keratotomy. The damage to
the cornea is reduced and the image quality is improved. This surgical
procedure is still experimental, the long term consequences of burning the
cornea are unknown and the procedure requires very costly and cumbersome
electro-optical apparatus.
OBJECT AND SUMMARY OF THE INVENTION
The object of this invention is to provide an improved means to correct all
refractive errors, myopia, hyperopia and astigmatism, with a simple
device. The device is much easier to use than the prior art. In contrast
to the prior art, this device alters the shape of the cornea by
plastically deforming it under the force created by a vacuum. The cornea
is not cut, burned or damaged. The cornea is stretched beyond its elastic
range, therefore it is plastically deformed permanently.
An object of this invention is to deform the areas of the cornea that are
placed under openings of a vacuum chamber. If the openings are elongated
in a given direction, it is shown below that the stress created by the
vacuum can deform those areas plastically in the perpendicular direction.
The device described by this invention stretches corneal tissue, called
stroma, in a preferential direction or pattern, creating a permanent
plastic deformation in that direction. When the vacuum chamber has
radially elongated openings that are uniformly spaced, myopia can be
corrected. When the vacuum chamber has circular or tangential openings,
hyperopia can be corrected. When the openings are not uniformly spaced
astigmatism can be corrected.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a preferred embodiment of the invention for the correction of
myopia. It depicts a vacuum chamber with ten openings in the form of
elongated circular sectors.
FIG. 2 shows a top view or projection of the openings of the vacuum chamber
in FIG. 1.
FIG. 3 shows a projection of alternative openings of the vacuum chamber in
the form of eight radial rectangles for the correction of myopia.
FIG. 4 shows a projection of alternative openings of the vacuum chamber in
the form of three rings for the correction of hyperopia.
FIG. 5 shows a projection of alternative openings of the vacuum chamber in
the form of eight tangential rectangles for the correction of hyperopia.
FIG. 6 illustrates how rectangular openings can produce a plastic
deformation in one direction.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is designed to correct refractive errors by altering
the shape of the cornea of the eye by means of a force created by a
vacuum. The method and means of the present invention is understood by
reference to FIG. 1. In this arrangement a vacuum chamber I is connected
to an ordinary vacuum pump 2 by some ordinary means, such as flexible
tubing. The vacuum chamber 1 is open in the top, as depicted in FIG. 1,
where several openings are present. There are ten interconnected openings
in FIG. 1, they are marked with numeral 3. The exact number of openings is
not important. The open side of the vacuum chamber is placed in contact
with the cornea of the eye. To this end, this side of the vacuum chamber
is shaped to approximately conform to the shape of the cornea. This side
is therefore of a spherical or quasi-spherical shape with a radius of
about 8 mm.
FIG. 2 shows this side as a top view or projection. When placed on the
cornea, the vacuum chamber 1 is fully closed by the surface of the cornea.
A vacuum then created by vacuum pump 2 will create a negative pressure and
suction force. This force will tend to distend the areas of the cornea
covering the openings towards the vacuum chamber. The net pressure is the
difference between the pressure (vacuum) created in the vacuum chamber by
the vacuum pump and the atmospheric and intraocular pressure together.
Since the atmospheric pressure is much greater than the intraocular
pressure, the atmospheric pressure is substantially the maximum pressure
that can be applied to the cornea with this device. All the openings apply
the same pressure to the areas of the cornea that they cover because they
are connected to the same vacuum pump by a common vacuum chamber. FIG. 2
shows in detail the openings 3 that are in contact with the cornea. They
are in the form of circular sections, except that the central area of the
chamber is in the form of a cylindrical hole or window 4, where no vacuum
is applied. In this way, the central part of the cornea is not stretched.
The force applied to the cornea at each opening by the vacuum tends to
push those areas of the cornea toward the vacuum chamber. Those areas of
the cornea in contact with the inside and outside circles and the
connecting spokes are not pushed inward.
A vacuum of such pressure is applied to the chamber so that the cornea
sections in contact with the openings deform beyond the elastic range,
that is, there is a plastic deformation of a permanent nature. As it will
be explained below, the deformation occurs in the direction perpendicular
to the elongated direction of the opening. It is known, and it can be
seen, that a permanent elongation of the cornea along circumferences
centered in the center or apex of the cornea causes the cornea to flatten
in the center. This is the desired result for the correction of myopia.
FIG. 3 depicts a variation of the vacuum chamber that achieves the same
result. Instead of openings in the form of circular sections, the openings
5 are rectangles. The form of the openings is not important, as long as
they are elongated in the radial direction for the correction of myopia.
To correct hyperopia, openings such as those depicted in FIG. 4 and FIG. 5
should be used. FIG. 4 shows circular openings 7, while FIG. 5 shows
tangential openings 8. In these configurations, the permanent deformation
or stretch of the cornea occurs in the radial direction. It is known that
such deformation causes the cornea to become steeper, that is, of a
smaller radius of curvature. This is the desired effect to correct
hyperopia.
FIGS. 3 to 5 depict the openings of the vacuum chamber as a top view or
projection. As in FIG. 1, the three-dimensional shape of the openings is
quasi spherical, so that it approximately conforms to the shape of the
cornea.
FIGS. 1 to 5 depict all openings equally spaced around the meridians of the
circumference. In this way the deformation of the cornea will be
circumferentially uniform. This is the desired result for the correction
of simple myopia and hyperopia. However, for the correction of
astigmatism, where the eye has different refractive power across the
meridians, the openings should be spaced unequally and in such a way as to
compensate the eye irregularity.
FIG. 6 depicts the deformation of the cornea placed in contact with the
openings in FIGS. 3 and 5 when a vacuum is applied. Letters a and b depict
the cross section of the cornea covered by the opening when no pressure is
applied. Letters a' and b' depict the cross section of the cornea covered
by the opening when pressure is applied. The same letters, a, b, a' and b'
are used below to denote the dimensions of a, b, a' and b' respectively.
It can be seen that the cos(.alpha.) is approximately equal to a/a' and
that cos(.beta.) is approximately equal to b/b' where a and b are the
dimensions of the rectangular opening, a' and b' are the dimensions of the
stretched cornea, and .alpha. and .beta. are the angles that the cornea
bends at the point of contact with the mid-points of the sides of the
opening. Since a>b by definition of a rectangular or elongated opening,
then .alpha.<.beta.. Since .alpha.<.beta., then cos(.alpha.)>cos(.beta.)
or (a'/a)<(b'/b). But a'/a and b'/b are the relative strain of the cornea
in the two main directions of the rectangular opening. The strain in the
direction of segment b is greater than in the direction of a. Therefore a
vacuum can be applied that will strain the cornea to the point of plastic
deformation in the direction of the short side of the rectangle, while
there is no permanent deformation in the perpendicular direction. This
analysis also applies to the opening in FIGS. 1, 2, and 4 because these
openings, though they are not rectangular, are elongated or approximately
rectangular.
Although elongated openings are preferred as the most effective way to
alter the shape of the cornea, this invention is not limited to elongated
openings. For example, circular openings that are arranged
circumferentially, as in FIGS. 3 and 5, can produce a net flattening of
the cornea. This is so because despite the fact that each opening produces
the same stretch in all directions, the flattening caused by the circular
stretch is greater than the steeping caused by the radial stretch.
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